Googling AB8902B4-09CA-4BB6-B78D-A8F59079A8D5 shows this ProcessID to be linked to thumbnail caches. The solution on the internet seems to be to give up on thumbnails entirely. Surely one can do better than that?

By using the handle list feature of Procexp I saw the process (select process, choose View → Lower Pane, look for "File" type entries) I saw in particular that the process had an open handle to this file:

My current estimate is that this must've been a problem with sigh.wmv in particular, as I generated this file by converting another video file to Windows Media Video through VLC; this file opened just fine in Windows Movie Maker, but the exporting of the relevant project hung at some point in the video.

There is a javascript hidden in a null key. You can delete the content of the key and be done with it. The key is a null value key and Microsoft does not know how to remove it but you can delete the contents.